Surface bio-erosion and structural alteration of colored and agricultural plastics induced by Scenedesmus dimorphus and Chlorella vulgaris.

Plastic pollution remains a major environmental challenge because synthetic polymers and their additives can resist biological degradation. This study investigated the early stage surface modification of commercially formulated plastics following exposure to the freshwater microalgae Scenedesmus dimorphus and Chlorella vulgaris. Transparent and pigmented polyethylene terephthalate (PET) bottles and agricultural low density polyethylene (LDPE) films were incubated with microalgal cultures for 100 days under controlled laboratory conditions. Changes in plastic mass and surface properties were evaluated using gravimetric measurements, Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). Weight loss varied among treatment and plastic combinations. Aligned Rank Transform analysis showed significant effects of treatment (F = 22.54, p < 0.001), plastic type (F = 2.50, p = 0.036), and their interaction (F = 3.81, p < 0.001). FTIR analysis indicated changes in carbonyl and aliphatic functional groups, consistent with oxidative surface modification. SEM observations showed surface roughening, cracks, cavities, and localized delamination after microalgal exposure. The magnitude of these changes varied among plastic formulations and microalgal treatments. The results indicate that S. dimorphus and C. vulgaris were associated with detectable physicochemical and morphological changes at the plastic surface during the 100 day incubation period. However, the observed changes represent early stage surface modification and do not demonstrate complete polymer biodegradation or mineralization. The findings highlight the importance of polymer formulation when evaluating microalgae plastic interactions and provide evidence for further investigation of microalgal surface associated plastic alteration.